That's an interesting point but look at it this way. Beef fat is about the same as human fat, but cows don't eat meat as we do. Put it this way, the most efficient method to store energy has virtually no relation with the natural diet of the animal that stores this energy. Consider the composition of all the different kinds of meat we eat, and compare that to all the different diets they eat. If it's the most efficient means to store energy, then most animals who do store energy would end up doing it this way, and they do. How good our diet is for us doesn't depend on how we store the energy it contains, but on the effect this food has on our health.

I believe animal fat - pretty much any kind - is the best kind of fat for humans. More than that, I believe animal fat is the best food for us. The argument is lengthy but I'll summarize it. It starts with our big brain and our small gut. It's the ETH, or expensive tissue hypothesis. Our brain got bigger, so something else must have gotten smaller to compensate - our gut took the hit. A large brain needs tons of fuel, a small gut is less efficient. The only kind of food that could both fuel a large brain and be easily digested is animal fat. Animal fat is already prepared so to speak into a form that can be used immediately with little effort. As you noted, animal fat requires no conversion into a different substance like cellulose would need if that was our diet, to store it and use it. We simply need to mash it up somehow and make the fatty acids available for metabolism. The conversion has already been done by the animals we eat. Animal fat is the only kind of energy that was and still is acquirable in abundant quantities with little to no processing. Now apply this whole idea over a couple million years and we end up with homo-sapiens-sapiens.

Eating large quantities of refined vegetable fats instead of animal fats would be akin to reverting to an earlier diet, one which we are no longer adapted to. Furthermore, the total quantity of vegetable fats we do eat today represents probably several orders of magnitude more vegetable fats than any animal has, does, or will ever eat naturally. There is probably no animal on this planet today - let alone humans - that is adapted to a diet that contains such large amounts of vegetable fats. That's because two things are needed for refined vegetable fats to exist: Agriculture, and processing.

As we all know from personal experience on this forum, refined carbohydrates make us fat, sick, weak and other nasty things. Since we can only eat two kinds of energy - fats and carbs - and since carbs make us sick, and since we can't digest the fiber within which the carbs and/or fats and/or protein are contained in plants, and since vegetable fats have never been part of our diet in any significant quantities until 2 minutes before midnight, it follows that the only form of energy that is absolutely suitable for us is animal fat.

Anyway, that's my opinion on the subject.